Question

an experiment consists of flipping a fair coin 4 times. What is the probability of obtaining at least one head?

Answer 1

$\mathbb P(X\ge1)=1-\mathbb P(X=0)$

The probability of getting 0 heads in 4 tosses (or equivalently, 4 tails) is $\dfrac1{2^4}=\dfrac1{16}$.

So the desired probability is

$1-\dfrac1{16}=\dfrac{15}{16}$